Best way to read thermocouple input on FPGA?

[Tentotheminus9]

Hi,

A friend of mine has a PC running LabView 7, along with a 'standard' PCI DAQ card. He is able to read the input voltage from a thermocouple, or read the temperature directly (using the DAQ VIs) with ease. However, when I connect my thermocouple to my external connector block (in turn connected to a PXI 7831R) I can't see any easy way of reading the thermocouple output. In the FPGA block diagram option, all I can do is open a reference to the anolgue input, but can't tell Labview that this is a voltage input, for example.

Whats the best way of reading the thermocouple with the FPGA?

Cheers,

Rob.

[SachaE]

Hi,

   thermocouples are rather small voltages. You're looking at then reduced code width with using the full range of the AI on the FPGA.

The 7831R can take in the voltage, however you're going to have to push the integer result up to the PC to a) convert to a proper voltage, and then b) convert to a temperature reading.

An example of this can be found here :

http://sine.ni.com/apps/we/niepd_web_display.display_epd4?p_guid=EA46CD7831B2263CE034080020E74861&p_...

with the linked URL for the tutorial here :

https://www.ni.com/en/shop/data-acquisition/advanced-data-acquisition-techniques-with-ni-r-series.ht...

I realise this is for the cRIO, however the principle still holds for the 7831R.

Have a look at the shipping example in the help->Find examples in LabVIEW for the Toolkits and Modules->FPGA->General->Basic I/O

This should get you up and running, but as I say, you're across the full range of the AI, so mv signals from a thermocouple aren't going to be great.

Thanks

Sacha Emery

National Instruments (UK)